This invention relates generally to providing a reliable bearing and seal system for sealed bearing rotary cone-type rock bits used in hard rock drilling to permit significant increases in the speed and load capability thereof, and more particularly relates to a load responsive elastically flexing bearing design that provides hydrodynamic lubrication of the loaded bearing surfaces in response to relative rotation, thereby permitting the bearing to carry heavier loads at higher speeds while generating less heat than prior art drill bit bearings, and permitting the bearing to be lubricated with liquid oil-type lubricants such as synthetic oils that provide improved compatibility with elastomeric seals compared to the greases presently used in rock bits.
Rotary drilling techniques are used to penetrate into the earth to create wells for obtaining oil and gas. In order to drill through the rock which is encountered in such endeavors, a drill bit is employed at the bottom of a hollow drill string.
A rotary cone-type rock bit is commonly used for such drilling. In such bit designs, rotary cones incorporating patterns of cutting teeth are mounted on support shaft structures at the lower extremity of the drill bit. When the bit is rotated, the rotary cones rotate about the shafts and roll upon the bottom of the bore hole, and the weight of the drill string acting through the cutting teeth causes the rock formation to be broken up into small cuttings. Drilling fluid is circulated down through the drill string and into the bottom of the bore hole to transport the cuttings back to the earth""s surface. An example of such well known prior art drill bits is shown in U.S. Pat. No. 5,456,327 to Denton et al.
Thrust and journal bearings are typically employed to transfer the weight of the drill string from the shaft to the rotary cone, and ball bearings are typically employed to retain the rotary cones to the shaft. A grease-type lubricant, pressure balanced to the annulus of the well bore, is provided to lubricate the bearings. Drill bit bearings are expected to operate under very harsh conditions which include elevated temperature, high loading, extreme impact, and complex movement between the rotary cone and the shaft. Due to the severe geometrical constraints the bearings are small. Relative to their small size, these bearings are severely loaded, and the bearing contact stresses reach extremely high levels. As a result, the bearings perform poorly when operated at higher speeds, especially when higher loads are employed, which limits life in hard rock drilling.
Conventional rock bit bearings operate in a boundary lubrication regime, and are lubricated with greases that are heavily loaded with solid lubricants such as graphite, molybdenum disulphide, powdered calcium fluoride, copper particles and various types of soap to help carry the heavy bearing loads. Examples of such greases are described in U.S. Pat. No. 4,358,384 to Newcomb and U.S. Pat. No. 5,015,401 to Landry.
An elastomeric rotary seal is used to establish dynamic sealed relation between the rotary cone and the shaft in order to retain the lubricant and exclude the highly abrasive drilling fluid. Examples of such seals are described in U.S. Pat. No. 3,765,495 to Murdoch et. al. and U.S. Pat. No. 4,610,319 to Kalsi. In addition to the bearings, rotary seals are also a weak link in the reliability and life of the bearing systems employed in high speed rotary cone bits. Firstly, the solid lubricants contained in rock bit bearing greases are highly abrasive to elastomeric rotary seals. Secondly, these seals are prone to wear due to the harsh abrasive drilling fluid environment within which the drill bit operates. Thirdly, as the speed increases, higher heat generation by the bearings and the rotary seal causes thermal degradation of the elastomer material of the seal. These factors, coupled with the higher seal wear rate associated with high speed operation, can lead to early seal failure, permitting abrasive invasion of the bearings, and rapid bearing failure which can in severe cases even lead to loss of the rotary cone down-hole.
In order to replace the drill bit at the end of its useful life, it is necessary to first pull the entire drill string from the well. The downtime associated with the lengthy round trips required for such bit replacement can be a major component of the cost of drilling a well, particularly in wells of great depth. A significant reduction in the cost of oil and gas drilling can therefore be obtained by improving the reliability and life of the bearing and seal system used in rotary cone rock bits.
It is an objective of the present invention to provide a reliable bearing and seal system for use in mechanical equipment subject to high bearing loads, such as sealed bearing rotary cone-type rock bits used in hard rock drilling.
It is another objective of this invention to provide compact hydrodynamically lubricated bearings that lower bearing friction to permit operation under higher loads and higher speeds while minimizing bearing wear, preventing seizure, and remaining effective even as wear occurs at the bearing interface.
It is another objective of this invention to reduce bearing generated heat to prevent heat-related degradation of lubricant, bearings, elastomer seals, and associated components.
It is another objective of this invention to provide a bearing that is capable of providing hydrodynamic lubrication of bearing surfaces while employing a grease-type lubricant containing a high content of solid lubricant particles.
It is another objective of this invention to provide bearings for sealed bearing rotary cone-type rock bits that can operate under high loading in a liquid oil-type lubricant environment, such as a synthetic oil.
It is another objective of this invention to provide a compact bearing that can withstand high shock loads while maintaining low friction operation.
It is another objective of this invention to provide a sealed bearing rotary cone-type rock bit that maintains the integrity of the sealed bearing system seals and bearings by employing a liquid oil-type lubricant such as a high viscosity synthetic oil.
It is another objective of this invention to provide a compact bearing that permits low friction operation over a wide range of loads.
From the standpoint of the basic concept, this invention provides an improved bearing design of generally ring-like form for supporting and guiding a relatively rotatable member. Elastically flexing regions are incorporated into the bearing structure to create undulations in the bearing surface in response to the load and pressure applied to the bearing surface, to create an initial hydrodynamic wedge angle with respect to the mating surface of the relatively rotatable member. The gradually converging geometry created by these undulations promotes a strong hydrodynamic action that wedges a lubricant film of a predictable magnitude into the dynamic interface between the bearing and the relatively rotatable member in response to relative rotation. This film physically separates the dynamic surfaces away from each other, thus minimizing the asperity contact, thus reducing friction, wear and the heat produced by the bearing, while permitting operation at higher load and speed combinations. The bearing of the present invention has a continuous ring shaped body of generally circular form that defines at least one dynamic surface, and defines a plurality of support regions each defining a static face oriented in generally opposed relation with the dynamic face. A plurality of flexing regions are defined by undercut regions between adjacent support regions, it being preferred that the undercut regions be open-ended; i.e. passing completely through the bearing beam-section width from side to side. Each of the flexing regions incorporates a first beam having a first hinge connection with one of the plurality of support regions, and incorporates a second beam having a second hinge connection with another of the support regions; and incorporates at least one local weakening geometry between the first and second beams that defines a flexing knee region interconnecting said first and second beams. The flexibility of the first and second hinges can be controlled by the thickness of the respective first and second beams, or by the use of a hole or a hinge-defining groove or recess. The flexibility of the hinges can also be controlled through material selection.
The at least one dynamic surface can be configured in a substantially cylindrical configuration forming an internal or external generally cylindrical shape for reacting radially oriented loads, and the at least one dynamic surface can be alternately configured in a substantially planar configuration for receiving axially oriented loads. The at least one dynamic surface can also consist of two dynamic surfaces in generally opposed relation, such as one of the dynamic surfaces being of substantially cylindrical internal form and the other being of substantially cylindrical external form to support radial loads, or such as both dynamic surfaces being of substantially planar form to support axial thrust loads.
The local weakening geometry that defines the flexing knee region can be of any suitable form, such as a recess, or a plurality of recesses, or such as a hole or a plurality of holes, or such as a combination of one or more recesses and one or more holes. The recesses forming the local weakening geometry can be of any suitable shape such as forming an open ended slot or a closed-end slot; for example the slot could extend completely across the width of the bearing, or the slot could be of generally round, oval (obround) or elliptical shape, or of an L-type shape. The recess could also be of variable depth; for example being deeper at one end than at the other with a view toward managing the flexibility of the flexible knee section across the radial width of a thrust bearing embodiment of the invention. The walls of the recess can be of any suitable angle, including being substantially perpendicular to a dynamic surface or angulated with respect to a dynamic surface. Likewise, any holes forming the local weakening geometry can be of any suitable shape and orientation; for example a hole could extend completely or partially through the local geometry of the bearing to form the local weakening geometry, and could be of generally round, oval (obround) or elliptical shape. The walls and general orientation of the hole can be of any suitable angle, including substantially perpendicular to a dynamic surface or angulated with respect to a dynamic surface, including being substantially parallel to a dynamic surface. When a plurality of holes and/or recesses are employed to form the local weakening geometry, they can be located relative to one another in any suitable manner, for example they can be located adjacent to one another, or in generally opposed relation to one another. If desired, the local weakening geometry can form one or more lubrication passages to provide a lubricant feed to the dynamic interface.
The first and second beams can be of any suitable shape for controlled deflection, such as having a substantially parallel thickness, or such as being tapered in a direction substantially in line with the direction of rotational velocity and/or a direction substantially normal with the direction of rotational velocity to obtain controlled flexibility. When the bearing of the present invention is used in a thrust bearing configuration, it is preferred that the sides of the first and second beams be of generally arcuate shape, and when it is used in a radial bearing configuration, it is preferred that the sides be of generally planar shape. It is further preferred that the intersection between the dynamic surface and sides of the first and second beams be broken, such as by a chamfer, a radius, or an elliptical shape. Even though the ratio of the mean circumferential length of the first beam divided by the mean circumferential length of the support region can vary widely, it should be between 2 and 3, and preferably about 2.5 for optimum hydrodynamic lubrication generation.
This invention provides a reliable bearing and seal system for high speed sealed bearing rotary cone-type rock bits by providing a load responsive elastically flexing bearing design that provides hydrodynamic lubrication of the loaded bearing surfaces while generating less heat and permitting the bearing to be lubricated with liquid lubricants such as liquid lubricating oils or synthetic lubricating oils that provide higher compatibility with elastomeric seals compared to the cohesive-type lubricant greases containing solids presently used in rock bits. In particular, the optimum bearing and seal system for a sealed bearing rotary cone-type rock bit is preferred to consist of one or more of the load responsive hydrodynamic bearings described above in conjunction with a resilient compression-type rotary seal that defines hydrodynamic geometry to wedge a hydrodynamic film of lubricant into the dynamic sealing interface between the seal and shaft to allow the seal to better accommodate the high drill bit rotary speeds associated with drilling through hard rock formations.
The drill bit construction under consideration herein is generally known as a rotary cone type rock bit. The body structure of the drill bit provides at least one and usually a plurality of arm structures (typically 3) each having support shafts projecting therefrom which provide support for a rotary cone having a cutting structure thereon. Thrust and journal bearings, at least one of which being of the hydrodynamic bearing configuration described above, are employed to guide the rotation of the rotary cone and to transfer the weight of the drill string from the shaft to the rotary cone.
When the bit is rotated, the rotary cones rotate against the bottom of the bore hole, and the weight of the drill string acting through the cutting structure causes the rock formation to be broken up into cuttings. Drilling fluid is circulated down through the drill string, thence through one or more drill bit orifices into the bottom of the bore hole to transport the cuttings back to the earth""s surface.
A lubricant is provided to lubricate the bearings. This lubricant may be a grease that is heavily loaded with solid lubricants such as graphite, molybdenum disulphide, powdered calcium fluoride, copper particles combined with one or more types of soap base, but in order to minimize rotary seal damage and thereby prolong the effective life of the drill bit bearings it is preferred that the lubricant be a liquid oil type lubricant, especially a high viscosity synthetic lubricant having a viscosity of 900 centistokes or more at 40xc2x0 C.
A ring-shaped rotary seal of any suitable configuration is used to establish a sealed relationship between the rotary cone and the shaft in order to retain the lubricant and exclude the drilling fluid. The preferred seal is a compression-type seal having a ring-like body formed from resilient material that establishes static sealing engagement with the rotary cone and establishes relatively rotatable interference sealing engagement with the shaft. The preferred seal also incorporates a dynamic sealing lip which defines an axially varying shape on the lubricant side thereof for promoting hydrodynamic wedging activity that wedges a lubricant film into the dynamic sealing interface in response to relative rotation, and which employs an abrupt non-axially varying shape on the drilling fluid side for excluding the drilling fluid. By the presence of the lubricant film, this seal configuration eliminates direct rubbing contact between the surface of the seal and the mating surface of the shaft, thereby allowing high speeds without undue heat generation and seal wear. Such seals are described in the prior art of U.S. Pat. Nos. 4,610,319, 5,230,520, 5,738,358, 5,873,576, 6,036,192, 6,109,618 and 6,120,036, said patents being incorporated herein by reference for all purposes. The rotary seal may be composed of any one of a number of suitable sealing materials including elastomeric or rubber-like sealing material and various other polymeric sealing materials, and combinations thereof.
By combining hydrodynamic bearings and hydrodynamic seals into a rotary cone rock bit, a synergistic bearing and seal system is provided that provides long bit life while accommodating high speed operation under heavily loaded conditions.
The bearing of this invention, although primarily designed for enhancing the wear capabilities of bearings used in rock bits, also has application in other types of rotary equipment, with either the bearing housing or the shaft, or both, being the rotary member. Examples of such equipment include but are not limited to downhole drilling motors, downhole rotary steerable equipment, rotary well control equipment, and equipment used in construction, mining, dredging, and pumps where bearings are heavily loaded.